PROEJCT SUMMARY/ABSTRACT African Americans (AAs) continue to have the highest incidence and mortality rates of colorectal cancer among all racial and ethnicity groups. To what extent differences in tumor biology contribute to the striking racial disparities remain largely unknown. Our team has recently completed the first genome-wide analysis of the mutational landscape of colorectal cancers specifically arising in AAs. This landmark study has identified a novel 15-gene mutation signature showing an over 3-fold increased mutation rate in AA colorectal cancers, and shown that 41% of AA colorectal cancers have somatic mutations in at least one of the 15 genes, which is significantly different from colorectal cancers derived from Caucasians. Furthermore, 14% of AA colorectal cancers harbor mutations seen exclusively in AAs, most prominently including the ephrin type A receptor 6 gene [EPHA6]. We further identified that these mutations convey a poor prognostic outcome in AA colorectal cancer patients. Building upon these discoveries, the current proposal tests our central hypothesis that inherent biological differences may in part be responsible for the disparate burden of colorectal cancer in AAs. In particular, we propose to: (Aim 1) validate and establish a novel mutation subtype of colorectal cancer arising from African ancestry genome and define the role of these mutations in AA colorectal cancer progression; (Aim 2) elucidate the clinical and etiological significance of the mutation signature in AA colorectal cancer; and (Aim 3) to define the functionality of AA colorectal cancer-derived EPHA6 mutations. The highly translational aims 1 and 2 will be accomplished by re-sequencing the 15-gene mutations in a large independent set of AA colorectal cancer patients (in comparison with Caucasian patients) who have annotated clinical and epidemiological information. We will use CRISPR/Cas9 and cutting-edge organoid technologies in aim 3 to define the functional significance of EPHA6 mutations derived from AA colorectal cancers. Our study will generate novel insight into the biological basis for racial disparities in colorectal cancer and inform tailored prevention and intervention strategies to reduce the burden of colorectal cancer in AA population.